I use it with the iPhone, and also with the iPad. However, I prefer the iPhone. The audible feedback is very good, ands it promotes good consistency in film developing.
My hands are not so wet, since I develop film in light tight tanks. The only contact with the phone is when changing from developer to stop bath, or from stop bath to fixer, then to hypo clear. You have to activate through the "continue" button, but you do not have to fumble for it.
I like the fact that it will adjust developing time according to your developer temperature (that you input by hand before starting).